Molecular characterization of a sweetpotato stress tolerance-associated GDP-L-galactose phosphorylase gene (IbGGP1) in response to abiotic stress

Ascorbic acid (AsA) can participate in the enzymatic and nonenzymatic clearance processes of reactive oxygen species (ROS), thereby enhancing stress tolerance in plants. GDP-L-galactose phosphorylase (GGP) is predicted to be a critical enzyme in the L-galactose route of plant AsA biosynthesis. However, information on the catalytic AsA synthesis and stress-resistance effect of the GGP gene in sweetpotato remains scarce. In this study, the IbGGP1 gene from sweetpotato was successfully isolated. The qRT-PCR determination revealed a distinctly higher expression level of IbGGP1 in sweetpotato flowers, and the gene was induced by multiple stresses, especially in drought, salt, and extreme temperatures. The seed germination, root elongation, and fresh weight were promoted in T₃ Arabidopsis IbGGP1-overexpressing lines as compared to wild-type plants under mannitol and salt stresses. The heterologous overexpression of IbGGP1 upregulated the mRNA level of the AtGME and AtGPP genes, and elevated the AsA content and AsA/DHA ratio under soil drought and salt stress. This stress-tolerance phenotype was associated with lower hydrogen peroxide and malondialdehyde content and higher antioxidant enzyme activity. These results indicate that the increased expression of IbGGP1 in Arabidopsis improves tolerance to multiple environmental stresses by promoting AsA biosynthesis and ROS-scavenging system. The functional identification of IbGGP1 provides a new approach for improving stress tolerance to drought and salt in sweetpotato and other species.